Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “AMINO ACIDS”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 37 records · Page 2Linked to original sources
PubMed1986

The transport of amino acids, amino acid derivatives and ions across ion-exchange membranes.

The passage of inorganic salts, glucose, amino acids and peptides across polystyrene-backed double membranes (negative-positive fixed-charge junctions) was studied in a two-compartment cell and compared to a known cellular system, the Ehrlich-Lettre ascites carcinoma. It was concluded that passage proceeds by a 1:1 exchange of diffusing ions in the membrane. The more rapidly transported systems reflected an increased probability of exchange in all cases, as evidenced both by a saturation effect and by the degree to which the space charge was perturbed at the membrane. The amino group (as NH3+) of the amino acid involved in the exchange process was vital for transport. The presence of a second amino group, either ionized or as -NH2, accelerated the exchange. The presence of electron-attracting groups on the side chain or of a methyl group on the alpha carbon also facilitated passage. Cation dependence was seen. Passage was hindered by a second carboxyl group, an alcoholic group, or a lengthened side chain. Use of double membranes permits experimental electrode transport modelling and may facilitate design of a drug delivery system.

Amino Acids↗
PubMed1985

Schistosoma mansoni, S. japonicum, and S. haematobium: permeability to acidic amino acids and effect of separated and unseparated adults.

Permeability of the tegument of male and female Schistosoma mansoni was measured in vitro and a comparison was made between copulating and separated worms. In unpaired (separated) schistosomes, a carrier-mediated (selective) transport system for acidic amino acids was demonstrated. Males and females exhibited similar uptake rates for aspartate and glutamate. Half-saturation constants for aspartate (males, 0.035 +/- 0.008 mM; females, 0.026 +/- 0.006 mM) and glutamate (males, 0.010 +/- 0.007 mM; females, 0.015 +/- 0.004 mM) were determined for separated worms only. Time-course studies provided estimates of aspartate influx rates in males (7.3 pmol min-1 worm-1) and females (2.3 pmol min-1 worm-1). The most dramatic observation, however, was that, in copula, neither male nor female schistosomes took up acidic amino acids, but may have excluded these compounds. Thus, this ouabain-insensitive, mediated mechanism was operational only when the worms were unmated. In S. japonicum, no uptake of glutamate was observed in either mated or separated males and females. In S. haematobium, saturable uptake of aspartate was apparent in both mated and unmated males and females, indicating that species-specific differences in uptake of acidic amino acids existed. These studies indicate the need for cautious interpretation of data obtained from in vitro analyses of separated male and female mansonian schistosomes, and that such conditions may not reflect in vivo or in copula function.

Animals↗
PubMed1980

Electrical evidence for different mechanisms of uptake for basic, neutral, and acidic amino acids in oat coleoptiles.

The application of neutral or acidic amino acids to oat coleptiles induced transient depolarizations of the membrane potentials. The depolarizations are considered to reflect H(+) -amino acid co-transport, and the spontaneous repolarizations are believed to be caused by subsequent electrogenic H(+) extrusion. The basic amino acids depolarized the cell membrane strongly, but the repolarizations were weak or absent. The depolarizations induced by the basic amino acids were weakly sensitive to manipulations of the extracellular and intracellular pH. The depolarizations induced by the other amino acids, in contrast, were more strongly affected by the pH changes. Several amino acids induced distinct but diminished depolarizations in the presence of 2,4-dinitrophenol or cyanide, but the repolarizations were generally eliminated. These experiments support the co-transport theory but suggest somewhat different mechanisms for the transport of the neutral, acidic, and basic amino acids. We suggest that the neutral amino acids are co-transported with a single H(+) and that accumulation depends upon both the DeltapH and the membrane potential components of the proton motive force. The acidic amino acids appear to be accumulated by a similar mechanism except that the transport of each molecule may be associated with a cation in addition to a single proton. The permanently protonated basic amino acids appear not to be co-transported with an additional proton. Accumulation would depend only on the membrane potential component of the proton motive force.

Journal Article↗
PubMed1991

Purification and amino acid sequence of a bitter gourd inhibitor against an acidic amino acid-specific endopeptidase of Streptomyces griseus.

An inhibitor (BGIA) against an acidic amino acid-specific endopeptidase of Streptomyces griseus (Glu S. griseus protease) was isolated from seeds of the bitter gourd Momordica charantia L., and its amino acid sequence was determined. The molecular weight of BGIA based on the amino acid sequence was calculated to be 7419. BGIA competitively inhibited Glu S. griseus protease with an inhibition constant (Ki) of 70 nM, and gel filtration analyses suggested that BGIA forms a 1:1 complex with this protease. However, two other acidic amino acid-specific endopeptidases, protease V8 from Staphylococcus aureus and Bacillus subtilis proteinase (Glu B. subtilis protease), were not inhibited by BGIA. BGIA had no inhibitory activity against chymotrypsin, trypsin, porcine pancreatic elastase, and papain, although subtilisin Carlsberg was strongly inhibited. The amino acid sequence of BGIA shows similarity to potato chymotrypsin inhibitor, barley subtilisin-chymotrypsin inhibitor CI-1 and CI-2, and leech eglin C, especially around the reactive site. Although the residue at the putative reactive site of these inhibitors is leucine or methionine, the corresponding amino acid in BGIA is alanine.

Amino Acid Sequence↗
PubMed1987

Transport of acidic amino acids by human jejunal brush-border membrane vesicles.

This study characterizes the transport of radiolabeled acidic amino acids into brush-border membrane vesicles prepared from human jejunum. The uptakes of L-glutamic, L-aspartic, and D-aspartic acids were stimulated by a Na+ gradient (extravesicular greater than intravesicular). Concentrative uptake (resulting in an "overshoot" phenomenon) of these dicarboxylic amino acids occurred when there was an outward K+ gradient (intravesicular greater than extravesicular). In addition, increasing K+ gradients (0-100 mM) resulted in enhanced uptake of L-glutamic acid. This K+ requirement is somewhat specific as Rb+ and Cs+ could enhance uptake to a limited extent, whereas Li+ and choline+ showed no enhancement. The presence of a K+ gradient did not affect the affinity of the carrier system for L-glutamic acid but it did increase the Vmax. The presence of extravesicular anions having differing membrane permeabilities did not alter L-glutamic acid uptake indicating an absence of an effect of membrane potential on the transport process. Finally, the human transport system for L-glutamic acid appears to be specific for acidic amino acids as demonstrated by inhibition studies. Our studies demonstrate a transport system in human jejunum specific for acidic amino acids that is energized by an inward Na+ gradient and an outward K+ gradient.

Aspartic Acid↗
PubMed2003

A functional gltB gene is essential for utilization of acidic amino acids and expression of periplasmic glutaminase/asparaginase (PGA) by Pseudomonas putida KT2440.

Pseudomonas putida KT2440, a root-colonizing fluorescent pseudomonad, is capable of utilizing acidic amino acids (Asp and Glu) and their amides (Asn and Gln) as its sole source of carbon and nitrogen. The uptake of Gln and Asn is facilitated by a periplasmic glutaminase/asparaginase (PGA), which hydrolyses Asn and Gln to the respective dicarboxylates. Here, we describe transposon mutagenesis of P. putida KT2440 with a self-cloning promoter probe vector, Tn 5-OT182. Transconjugants defective in Glu-mediated PGA induction were selected for further studies. In most clones the transposon was found to have integrated into the gltB gene, which encodes the major subunit of the glutamate synthase (GOGAT). The transconjugants were nonmotile, no longer showed a chemotactic response towards amino acids, and could not survive prolonged periods of starvation. The acidic amino acids and their amides supported growth of the transconjugants only when supplied together with glucose, suggesting that the gltB-mutants had lost the ability to utilize amino acids as a carbon source. To confirm that gltB inactivation was the cause of this phenotype, we constructed a mutant with a targeted disruption of gltB. This strain behaved like the clones obtained by random mutagenesis, and failed to express not only PGA but also a number of other Glu-induced proteins. In contrast to wild-type cells, the gltB(-) strain accumulated considerable amounts of both Glu and Gln during long-term incubation.

Amidohydrolases↗
PubMed1982

Putative acidic amino acid transmitters in the cerebellum. I. Depolarization-induced release.

In the present investigation we studied the autoradiographic localization and the characteristics of the depolarization-induced release of acidic amino acids in in vitro rat cerebellar preparations. Light microscopy autoradiography of cerebellar slices preincubated in the presence of the non-metabolized glutamate analogue D-[3H]aspartate showed a large accumulation of radioactivity over glial cells, and very little labelling of the granule cells, whose putative neurotransmitter may be glutamate. In spite of its predominant localization in glia, D-[3H]aspartate (and [14C]glutamate) was released from cerebellar slices depolarized with high [K+] in a Ca2+-dependent way, and the release elicited by veratrine was prevented by TTX. These findings, together with the observation that freshly isolated or cultured glial cells did not show any Ca2+-dependent, depolarization-induced release of D-[3H]aspartate, suggest that the radioactive amino acid released from slices has a neuronal origin. The high [K+]-induced release of exogenous radioactive acidic amino acids from superfused cerebellar synaptosomal preparations exhibited, as best, a modest Ca2+-dependence, a result probably due to the existence of a substantial non-Ca2+-dependent release of the amino acid from glial fragments contaminating the preparation. However, both the K+-evoked release of endogenous glutamate, and that of [14C]glutamate previously synthesized from [14C]glutamine were largely Ca2+-dependent, suggesting that nerve endings are the main sites involved in the stimulus-coupled secretion. In the experiments in which synaptosomes had been prelabelled with [14C]glutamine, a study of the specific radioactivity of the glutamate released and of that present in synaptosomes at the beginning and at the end of superfusion period provided evidence in favour of a preferential release of the newly synthesized [14C]glutamate. In contrast to glutamate, endogenous aspartate was not released in a Ca2+-dependent manner, and the efflux of newly formed [14C]aspartate was only slightly potentiated by Ca2+, which suggests that glutamate and aspartate are not released from the same sites. Studies on preparations (slices and synaptosomes) from immature, 8-day-old cerebella showed that neither the K+-evoked release of D-[3H]aspartate, nor that of endogenous glutamate was Ca2+-dependent. In conclusion, the data presented are consistent with the proposition that glutamate has a neurotransmitter role in the cerebellum.U

Amino Acids↗
PubMed1995

The entry of acidic amino acids into brain and CSF during development, using in situ perfusion in the rat.

Previous studies using the rapid single pass blood to tissue uptake of substances by the capillaries of the blood-brain barrier, have failed to show significant uptake of acidic amino acids. However, by the use of a bilateral in situ brain perfusion in neonatal and adult rats, extending the perfusion time to 30 min, the carrier-mediated uptake of aspartate and glutamate into brain and CSF has been demonstrated. The ratios of 14C-acidic amino acids in the brain and CSF to that in perfusate were measured and represented as Rbrain and RCSF respectively, after 30 min, neonatal (1-week-old) Rbrain values for both amino acids were approximately twice that of adults, while neonatal RCSF for aspartate and glutamate were 3 to 5 times that of the adult. In contrast, there was no significant entry of NMDA into either compartment for both adults and neonates. The transfer coefficient, Kin into brain and CSF was also measured in relation to stages of development. In general the Kin values for brain and CSF for aspartate and glutamate were higher in the younger age groups than the adult group (1 week > 2 week > 3 week > or = adult). In 1- and 2-week-old rats entry into CSF appears to be higher than that of brain, whereas for adults entry into the brain tissue was dominant.

Animals↗
PubMed1994

Role of acidic amino acids in the allosteric modulation by gallamine of antagonist binding at the m2 muscarinic acetylcholine receptor.

The purpose of this study was to explore the role of acidic amino acids in the allosteric behavior of gallamine at the m2 receptor. This was achieved by first mutating the acidic residues to neutral residues by site-directed mutagenesis. Both the parent and mutated receptors were expressed in mouse fibroblast A9L cells and characterized pharmacologically. The two main methods used were (i) Schild analysis of equilibrium binding data and (ii) study of the effect of gallamine on the dissociation kinetics of N-methylscopolamine. The Schild analysis gave an estimate of the affinity of gallamine for the allosteric site (KdA) and also a measure of the level of cooperativity (alpha) between the allosteric and primary binding sites. For the receptors studied, a good agreement was found between the alpha KdA values calculated from the Schild analysis and the IC50 values for the effect of gallamine on the N-methylscopolamine off-rate. One mutated receptor, in which the acidic EDGE (Glu-Asp-Gly-Glu) sequence of the putative third outer domain was changed to the neutral LAGQ (Leu-Ala-Gly-Gin) sequence, displayed an 8-fold reduction in affinity for gallamine at the allosteric site, in comparison with the parent receptor. The level of cooperatively between the allosteric and primary binding sites in this mutant was 46% of that of the parent receptor. A second mutated receptor, in which Asp-97 (near the top of putative transmembrane domain 3) was changed to asparagine, was found to have a level of cooperativity between sites 58% of that of the parent but was found not to be affected with respect to the affinity of gallamine for the allosteric site. When all of the acidic groups on the outer side were changed to neutral residues, there was still only an 8.6-fold reduction in gallamine affinity for the allosteric site, but the level of cooperativity was reduced to 19% of that found in the parent receptor. The results suggest that the allosteric site for gallamine binding in the m2 receptor residues at or near the putative third outer domain and that both the EDGE motif and Asp-97 play an essential role in the interaction between the two sites. However, none of the acidic amino acids mutated were found to be critical for binding at the allosteric site.

Allosteric Regulation↗
PubMed1967

Loss of organic acids, amino acids, k, and cl from barley roots treated anaerobically and with metabolic inhibitors.

Excised roots of barley (Hordeum vulgare, var. Campana) lost organic acids, amino acids, K(+), and Cl(-) within 15 minutes after initiation of anaerobic treatment or treatment with NaCN and 2,4-dinitrophenol. Initial loss of organic acids when roots were placed under N(2) is attributed to a decarboxylation reaction, possibly catalyzed by phosphoenolpyruvate carboxykinase. Organic and amino acids began to leak from the roots to the bathing medium after 1 to 2 hours under N(2), indicating injury to cell membranes. During the first hour of anaerobic treatment, K(+) loss from low-salt roots was equivalent to organic acid loss. Potassium loss from roots containing high levels of KCl was approximately equal to organic acid plus amino acid loss; and Cl(-) loss was approximately equal to amino acid loss. It is postulated that, within cells, organic acids may electrostatically bind an equivalent quantity of cations and that amino acids may bind an equivalent quantity of both cations and anions.

Journal Article↗
PubMed2000

Acidic amino acid clearance from CSF in the neonatal versus adult rat using ventriculo-cisternal perfusion.

The acidic amino acids aspartate and glutamate are excitatory neurotransmitters in the CNS. The clearance of this group of amino acids from CSF of adult and neonatal (7-day-old) rats was investigated. Ventriculo-cisternal perfusions with 14C-amino acids and 3H-dextran were carried out for up to 90 min. Uptake of the amino acids by the whole brain was measured, and the loss to blood was calculated. 3H-Dextran was included in the perfusate for measurement of CSF secretion rate. After 90-min perfusion, both aspartate and glutamate showed a similar uptake into the whole brain, and this did not change with age (p>0.05). However, clearance from CSF was greater in the adult, as was entry into blood from CSF. Addition of 5 mM excess unlabelled amino acid resulted in reduction in the brain uptake of both 14C-amino acids in the adult rat. In the neonate, addition of aspartate also reduced brain aspartate uptake, whereas addition of glutamate increased brain neonatal [14C]glutamate uptake. The rate of CSF secretion was significantly greater in the adult, 1.26+/-0.18 microl x min(-1) x g(-1), than in the neonate, 0.62+/-0.08 microl x min(-1) x g(-1), and the turnover of CSF was greater in adults (p<0.01). In summary, both aspartate and glutamate showed greater clearances from CSF in the adult than the neonate. This clearance was found to be by carrier-mediated mechanisms.

Aging↗
PubMed1984

Depolarization of feline primary afferent fibres by acidic amino acids.

When administered micro-electrophoretically into the spinal grey matter of cats anaesthetized with pentobarbitone, acidic amino acids known to be neuronal excitants lower the threshold of electrically stimulated muscle and cutaneous primary afferent fibres and terminations. This depolarizing effect was not observed with fibres stimulated in the white matter. Depolarization by micro-electrophoretic potassium and excitant amino acids appeared not be be associated with an alteration in terminal membrane conductance since there was no change in synaptically evoked primary afferent depolarization. Excitant amino acid depolarization was not blocked by the gamma-aminobutyric acid antagonist bicuculline methochloride, but was reduced by selective excitant amino acid antagonists. The results are discussed in relation to the probable absence of specific excitant amino acid receptors on afferent terminals, the depolarizing effect of the amino acids on myelinated fibres and non-myelinated terminals being more likely a consequence of changes in the extracellular medium associated with the depolarization and firing of neurones.

Action Potentials↗
PubMed1989

Gostatin blocks physiological actions and binding of acidic amino acids in rat brain.

Gostatin, an inhibitor of aspartate aminotransferases isolated from Streptomyces sumanensis NK-23, was tested as an antagonist of acidic amino acid-mediated responses in the in vitro hippocampal slice and of acidic amino acid binding. Gostatin blocked responses to N-methyl-aspartate (AMPA) or L-glutamate. Gostatin also displaced N-methyl-D-aspartate-sensitive [3H]-L-glutamate binding (Ki = 22.0 microM) more potently than [3H]-kainate binding. Gostatin appears to be a relatively nonselective acidic amino acid antagonist in the mammalian central nervous system.

Amino Acids↗
PubMed1986

Transport of acidic amino acids by the bovine pigment epithelium.

The regulation of acidic amino-acid transport across the retinal pigment epithelium is of particular interest since glutamate and possibly aspartate have been identified as putative neurotransmitters in the retina, at the level of the photoreceptor cell. The present study, designed to measure the rate of acidic amino-acid transport across the mammalian pigment epithelium (PE), shows that there is a net transport of both glutamate and aspartate in the retina to choroid direction (R-C), with the R-C unidirectional flux of glutamate being substantially larger than the corresponding aspartate flux. The R-C and C-R fluxes of glutamate were found to be inhibited by ouabain. Further investigations utilizing aspartate revealed that the fluxes in both directions were inhibited when ouabain was present on the retinal side of the tissue preparation. The R-C flux of glutamate was significantly reduced by lowered concentrations of Na+, K+ and Ca2+, whereas the C-R flux was diminished only by the reduced concentration Ca2+. The changes in K+ concentration which markedly altered the R-C flux of glutamate were within the range of light-induced changes of K+ which has been observed in the extracellular space of the photoreceptor cells. The transporting system appears to be relatively specific for the acidic amino acids; for aspartate was an effective competitive inhibitor of glutamate transport whereas basic (lysine) and neutral (leucine) amino acids were not. The directionality, ouabain sensitivity, ionic dependence and substrate specificity of the transmembrane fluxes tend to support the concept of active transport as a mechanism of acidic amino-acid removal from the neural retina.

Amino Acids↗
PubMed2001

Role of acidic amino acid residues of PsaD subunit on limiting the affinity of photosystem I for ferredoxin.

The PsaD subunit of photosystem I is one of the central polypeptides for the interaction with ferredoxin, its acidic electron acceptor. In the cyanobacterium Synechocystis 6803, this role is partly performed by a sequence extending approximately from histidine 97 to arginine 119, close to the C-terminus. In the present work, acidic amino acids D100, E105, and E109 are shown to moderate the affinity of Photosystem I for ferredoxin. Most single replacements of these residues by neutral amino acids increased the affinity for ferredoxin, resulting in a dissociation constant as low as 0.015 microM for the E105Q mutant (wild-type K(D) = 0.4 microM). This is the first report on the limitation of photosystem I affinity for ferredoxin due to acidic amino acids from PsaD subunit. It highlights the occurrence of a negative control on the binding during the formation of transient complexes between electron carriers.

Amino Acid Sequence↗
PubMed1997

Evaluation of the role of specific acidic amino acid residues in electron transfer between the flavodoxin and cytochrome c3 from Desulfovibrio vulgaris.

A hypothetical model for electron transfer complex between cytochrome c3 and the flavodoxin from the sulfate-reducing bacteria Desulfovibrio vulgaris has been proposed, based on electrostatic potential field calculations and NMR data [Stewart, D. E., LeGall, J. , Moura, I., Moura, J. J. G., Peck, H. D., Jr., Xavier, A. V., Weiner, P. K., & Wampler, J. E. (1988) Biochemistry 27, 2444-2450]. This modeled complex relies primarily on the formation of five ion pairs between lysine residues of the cytochrome and acidic residues surrounding the flavin mononucleotide cofactor of the flavodoxin. In this study, the role of several acidic residues of the flavodoxin in the formation of this complex and in electron transfer between these two proteins was evaluated. A total of 17 flavodoxin mutants were studied in which 10 acidic amino acids--Asp62, Asp63, Glu66, Asp69, Asp70, Asp95, Glu99, Asp106, Asp127, and Asp129--had been permanently neutralized either individually or in various combinations by substitution with their amide amino acid equivalent (i.e., asparate to asparagine, glutamate to glutamine) through site-directed mutagenesis. The kinetic data for the transfer of electrons from reduced cytochrome c3 to the various flavodoxin mutants do not conform well to a simple bimolecular mechanism involving the formation of an intermediate electron transfer complex. Instead, a minimal electron transfer mechanism is proposed in which an initial complex is formed that is stabilized by intermolecular electrostatic interactions but is relatively inefficient in terms of electron transfer. This step is followed by a rate-limiting reorganization of that complex leading to efficient electron transfer. The apparent rate of this reorganization step was enhanced by the disruption of the initial electrostatic interactions through the neutralization of certain acidic amino acid residues leading to faster overall observed electron transfer rates at low ionic strengths. Of the five acidic residues involved in ion pairing in the modeled complex proposed by Stewart et al. (1988), the kinetic data strongly implicate Asp62, Glu66, and Asp95 in the formation of the electrostatic interactions that control electron transfer. Less certainty is provided by this study for the involvement of Asp69 and Asp129, although the data do not exclude their participation. It was not possible to determine whether the modeled complex represents the optimal configuration for electron transfer obtained after the reorganization step or actually represents the initial complex. The data do provide evidence for the importance of electrostatic interactions in electron transfer between these two proteins and for the existence of alternative binding modes involving acidic residues on the surface of the flavodoxin other than those proposed in that model.

Amino Acids, Dicarboxylic↗
PubMed2002

Response of forage fiber degradation by ruminal microorganisms to branched-chain volatile fatty acids, amino acids, and dipeptides.

This study evaluated the effect of branched-chain volatile fatty acids (VFA; isobutyric acid, isovaleric acid), amino acids (valine, leucine), and dipeptides (valine-valine, leucine-leucine) on neutral detergent fiber (NDF) degradation by rumen microorganisms in vitro. The CP (%) and in situ NDF degradation rate (%/h) for alfalfa, bermudagrass, and pangolagrass hays, and napiergrass silage were 17.2 and 7.5, 4.7 and 3.1, 8.3 and 5.3, and 9.6 and 3.4, respectively. In vitro NDF digestibility was the lowest for bermudagrass; alfalfa and napiergrass were the highest. When the incubation contained more ammonia initially, digestibilities increased, but relative differences among forages were unchanged. Adding branched-chain VFA (2 mM) to incubations increased digestibilities more than controls on 15 out of 16 occasions. The effectiveness varied with isoacids and forages used. Amino acid (2 mM) or dipeptide (1 mM) addition consistently increased digestibility over controls. Amino acids further increased digestibility over corresponding isoacids on 14 occasions. Improvement in digestibility over control by leucine appeared to be greater than that by valine. Digestibilities with dipeptides were always greater than those with isoacids, except for one case. Dipeptide addition further increased digestibility significantly over corresponding amino acids on only six occasions, while percent improvement in digestibility numerically by dipeptides occurred in 10 cases. Valine-valine seemed to exert different effect than leucine-leucine, depending on initial ammonia availability. The results indicate that dipeptides could be more effective than isoacids and amino acids in improving NDF digestion. Forages with high CP content or rapid NDF degradation rate appeared to respond to additives to smaller degrees.

Amino Acids↗
PubMed1986

The binding of acidic amino acids to snail, Helix aspersa, periesophagic ring membranes reveals a single high-affinity glutamate/kainate site.

The characterization of specific acidic amino acid binding sites to snail, Helix aspersa, ganglia membranes has been assayed using tritiated glutamate (L-[3H]Glu), aspartate (L-[3H]Asp), cysteine sulfinate (L-[3H]CSA) and kainate. At 2 degrees C, only L-[3H]Glu and [3H]kainate specific binding could be measured using a filtration procedure to separate bound from free ligand. The analysis of L-[3H]Glu specific binding reveals the presence of one class of high-affinity binding sites with Kd = 0.12 microM and Bmax = 30 pmol/mg protein. This L-[3H]Glu binding was specific, reversible and saturable. The order of potency of different substances, agonists or antagonists of the rat brain excitatory amino acid receptors, has been determined. Kainate was the best displacing agent, followed by ibotenate = L-Glu greater than L-alpha-aminoadipate (L-alpha-AA) greater than homocysteate (HCA). Using 10 nM [3H]kainate, a single class of binding site was detected. Its pharmacological properties indicate that it is likely identical to the L-[3H]Glu binding site. This L-Glu-kainate site possesses most of the properties expected for a specific receptor. However, whereas L-[3H]Glu binding could be detected on purified neuronal membranes, the major component of specifically bound L-[3H]Glu appeared to be located on the sheaths surrounding neuronal cell bodies. These findings suggest that Glu or another endogenous acidic amino acid may function as a transmitter at neuromuscular junctions in Helix periesophagic ring, acting at a receptor distinct from those on nerve cells.

Amino Acids↗